This invention relates to a piston sleeve with a mid stop, for a high compression engine, and a contoured bore that becomes a cylindrical bore under operating conditions.
Piston sleeves employed in high compression engines have generally had a flange on their top or head end that is clamped in place between the block and the cylinder head. The skirt of these piston sleeves is permitted to float due to thermal expansion and contraction. The elongation and contraction of piston sleeves that are dry has not been a problem. However cooling capacity must be somewhat larger with dry sleeves than with wet sleeves to insure adequate cooling.
High compression engines designed in recent years have generally had wet piston sleeves to improve cooling, reduce the coolant capacity requirement for their cooling systems and thereby reduce vehicle weight.
Piston sleeves with a top flange, as described above, that are in direct contact with engine coolant require sealing devices to seal between the sleeve skirt and the block. Such seals have durability problems. These durability problems are caused by movement between sleeve skirts and engine blocks due to thermal changes, engine vibrations, corrosion on the wet side of the sleeves, cavitation, seal material degeneration and other causes. Any leakage of coolant with antifreeze into an engine crankcase is a potential disaster. The water will be turned to vapor by crankcase heat and expelled from the crankcase. The antifreeze will not evaporate and therefore remains in the engine. Antifreeze is incompatible with engine lubrication systems and will cause moving parts to seize. Piston sleeve seal devices generally have a moderate failure rate during their first six thousand hours of operation or so. The seal device failure rate generally becomes unacceptable above ten thousand hours or so.
Engine designers are now designing engines with wet piston sleeves, each of which is anchored on the block by a radially extending flange that is mid way between the top end and the crankshaft or bottom end. The radially extending flange has an axial positioning surface in direct contact with a stop surface on the engine block. The sleeve is axially loaded between the cylinder head and the engine block stop surface to eliminate leakage of gasses and coolant. As a result, a seal device is not required between the block stop surface and the radially extending flange mid way between the sleeve ends. However, an appropriate seal device can also be employed if desired.
The axial load required to seal between a piston sleeve and the cylinder head and a block stop surface is substantial. The seal between the top end of the sleeve and the cylinder head must prevent the passage of compressed air prior to combustion and the pressure of hot gasses following combustion. In high output diesel engines that are turbocharged, the pressure in the combustion chamber is substantial. The seal between the axial positioning surface and the block stop surface generally does not require a large axial load. However, both seals must maintain a seal when the engine is cold as well as when the engine is hot.
The axial load on a piston sleeve with a mid stop that is required to prevent leakage between the top of a sleeve and a cylinder head and to prevent leakage between an axial positioning surface on the radial flange and a block stop surface under all possible operating conditions is large. An axial load on the piston sleeve that prevents leakage of gas and coolant, under a full range of operating conditions, distorts the inside walls of the piston sleeve. This distortion of the walls increases the rate of sleeve wall, piston and piston ring wear. The distortion also increases oil consumption, blow by, emissions of undesirable materials, and will eventually result in power loss. To minimize piston ring wear and all of the associated problems, the inside walls of the piston sleeves should be cylindrical or close to cylindrical under normal operating conditions.
One solution to the piston sleeve distortion problem has been proposed. This proposed solution is to provide thicker sleeve walls from the top edge to the mid stop. Thicker sleeve walls increases the weight of each sleeve and thereby increases the engine weight. A sleeve with an increased outside diameter requires a larger bore in the engine block. An increase in the diameter of the bores in the engine block will generally make it necessary to increase both the length and the width of the block to accommodate the larger bores for the piston sleeves and maintain coolant capacity. Increasing the block size obviously increases block weight and will generally make it necessary to increase the size and weight of other engine components.
The piston sleeve for a high compression internal combustion engine is a tubular member. The tubular member has a top surface, that is perpendicular to an axis of the tubular member, and a bottom surface. A radial positioning surface is adjacent to the top surface. An axial positioning surface faces axially toward the bottom surface and is between the top surface and the bottom surface. A radially outward facing coolant contact surface is between the radial positioning surface and the axial positioning surface. A skirt extends from the axial positioning surface to the bottom surface. A profiled radially inward facing surface extends substantially from the top surface to the bottom surface. The profile becomes substantially cylindrical when the piston sleeve is in a high compression internal combustion engine block and a predetermined axial compression force is applied to the top surface and to the axial positioning surface.
The piston sleeve provides a joint between its top surface and a cylinder head that holds products of combustion in the combustion chamber. Contact between the axial positioning surface of the piston sleeve and the engine block retains engine coolant and keeps coolant out of the crankcase without the use of a seal device. The cylindrical cylinder wall surface that is formed inside the sleeve during normal operation reduces piston ring wear, piston wear and sleeve wear. The cylindrical surface also reduces oil consumption blow by and undesirable emissions from the engine.
Piston sleeves for diesel engines with profiled cylinder walls as described above can be pressed into an internal combustion engine and ready to use as received from the factory. Expensive and time consuming honeing, polishing and cutting operations in the field are eliminated.